Thermoplastic elastomer composition and molded articles made thereof

ABSTRACT

The subject invention relates to a thermoplastic elastomer composition that contains a dynamically vulcanized thermoplastic elastomer (a) on the basis of a polypropylene polymer and an at least partly dynamically vulcanized rubber, a thermoplastic polyester block copolymer (b) and a compatibilizer (c). The rubber is preferably an EPDM or EPM copolymer. The thermoplastic polyester block copolymer is preferably a polyether ester block copolymer. The thermoplastic elastomer composition according to the invention for instance contains 20-80 parts (a), 80-20 parts (b), and 1-40 parts (c), the sum of the parts (a+b+c) being 100.  
     The thermoplastic elastomer composition according to the invention also relates to molded articles that contains the thermoplastic elastomer composition.

[0001] The invention relates to a thermoplastic elastomer composition,and molded parts thereof.

[0002] A thermoplastic elastomer composition is known inter alia fromPolymer Blends, Volume 2: Performance, edited by D. R. Paul and C. B.Bucknall, ISBN 0-471-35280-2, 2000. This article describes thermoplasticelastomers on the basis of a thermoplastic polymer and a dynamicallyvulcanized rubber which is dispersed in a continuous phase of thethermoplastic polymer in the form of fine particles. Such thermoplasticelastomers, thermoplastic vulcanisates, hereinafter called (TPV's),possess a number of properties of an elastomer and can be processedamong other things as a thermoplastic polymer.

[0003] The most widely used TPV's have a polyolefin as thermoplasticpolymer. As a consequence, these TPV's adhere only to apolar substratesand they do not adhere, or only with difficulty, to polar substrates. Toimprove the adhesion, the substrate is often pretreated. Industriallyused pretreatment methods are dependent on the substrate and may forinstance be chromic acid etching, ozone treatment, UV irradiation,primer coatings or plasma treatment. However, these pretreatments areexpensive, use hazardous substances, result in product degradation andinvolve environmental risks.

[0004] The aim of the present invention is to provide a thermoplasticelastomer composition that exhibits intrinsically good adhesion to polarand apolar substrates while it does not have the above-mentioneddisadvantages.

[0005] This aim is achieved according to the invention with athermoplastic elastomer composition that contains a blend of:

[0006] a. a dynamically vulcanized thermoplastic elastomer containing apolypropylene polymer and an at least partly dynamically vulcanizedrubber

[0007] b. a thermoplastic polyester block copolymer

[0008] c. a compatibilizer.

[0009] It has, surprisingly, been found that the thermoplastic elastomercomposition according to the invention exhibits particular good adhesionboth to apolar and to polar substrates, whereby it is possible to leaveout the pretreatment of the substrate.

[0010] A further advantage is that the thermoplastic elastomercomposition is obtained with a relatively low hardness and goodmechanical properties. Yet another advantage is that the thermoplasticelastomer composition according to the invention shows a good chemicalresistance towards several chemicals. Yet another advantage is thatmolded articles from the composition according to the invention show avery good grip and soft touch, which makes the thermoplastic elastomercomposition very suitable for the production of for example hand grips.From U.S. Pat. No. 5,149,589, a composition is known comprising athermoplastic elastomer and a copolyester. However the composition onlyshows a good adhesion to polar substrates. The composition has no goodresistance to chemicals. Moreover the molded articles have no good gripand soft touch.

[0011] Examples of suitable polypropylene polymers used in thethermoplastic elastomer composition according to the invention arethermoplastic polypropylene homo- and copolymers or blends thereof.Examples are polypropylene homopolymers or polypropylene copolymers withmax 30% polyethylene or copolymers of propylene and an alpha-olefin with4-12 carbon atoms. Preferably the polypropylene homopolymer is used. Thepolypropylene may be atactic, isotactic, syndiotactic or a physical andchemical mixture thereof. The term chemical mixture means that thepolypropylene may have atactic, isotactic or syndiotactic structuresrandomly or in blocks along the molecular chains. The polypropylenehomopolymer may be linear or branched. The Melt flow index (MFI) of thepolypropylene preferably is between 0.3 and 50; more preferably below 20(according to ISO norm 1133 (230° C.; 2.16 kg load)).

[0012] Examples of rubbers that can be used in the thermoplasticelastomer composition according to the invention are rubbers that aresuitable for dynamic vulcanization. Examples of such rubbers areethylene-propylene copolymers, hereinafter called EPM,ethylene-propylene-diene terpolymers, hereinafter called EPDM, styrenebutadiene rubber, nitrile butadiene rubber, isobutene-isoprene rubber,styrene-ethylene/styrene-butadiene block copolymers, butyl rubber,isobutylene-p-methylstyrene copolymers or brominatedisobutylene-p-methylstyrene copolymers, natural rubber or blends ofthese.

[0013] Preferably, EPDM or EPM is used as rubber. Most preferably, EPDMis used as rubber. The EPDM preferably contains 50-70 parts by weightethylene monomer units, 48-30 parts by weight monomer units originatingfrom an alpha-olefin and 2-12 parts by weight monomer units originatingfrom a non-conjugated diene. As alpha-olefin use is preferably made ofpropylene. As non-conjugated diene use is preferably made ofdicyclopentadiene (DCPD), 5-ethylidene-2-norbornene (ENB) orvinylnorbornene (VNB).

[0014] The dynamic vulcanization of the rubber is carried out in thepresence of a suitable vulcanization agent such as for instance sulfur,sulfurous compounds, metal oxides, maleimides, phenol resins orperoxides. These vulcanization systems are known from the state of theart and are described in U.S. Pat. No. 5,100,947. It is also possible touse siloxane compounds as vulcanization agent, examples are hydrosilaneor vinylalkoxysilane. The thermoplastic elastomer composition accordingto the invention is preferably vulcanized with the aid of phenol resins,siloxanes or peroxides as vulcanization agent. The degree ofvulcanization can be expressed in terms of gel content. This method isdescribed in U.S. Pat. No. 5,100,947.

[0015] The rubber in the thermoplastic elastomer composition accordingto the invention is at least partly vulcanized and for instance has agel content between 60 and 100%. More preferably, the rubber has a gelcontent between 80 and 100%. Most preferably, the rubber is fullyvulcanized and has a gel content in excess of 95%.

[0016] The polyester block copolymer used in the thermoplastic elastomercomposition according to the invention preferably consists of softblocks of a flexible polymer segment and hard blocks of a non flexiblepolymer segment.

[0017] The soft blocks of the flexible polymer segments for instancehave a molecular mass of 400-6000 g/mol; preferably they have amolecular mass of 500-3000 g/mol. Examples of soft blocks are aliphaticpolyether segments or aliphatic polyester segments. Examples ofaliphatic polyester segments are polybutylene adipate segments orpolycaprolactone segments. Examples of aliphatic polyether segments arepolyalkylene-oxide glycol segments such as for instancepolyethylene-oxide glycol segments, polypropylene-oxide glycol segment,polytetramethylene-oxide glycol segments or ethylene oxide-terminatedpolypropylene-oxide glycol segments.

[0018] Preferably, an aliphatic polyether segment is used as soft blockin the polyester block copolymer. More preferably, ethyleneoxide-terminated polypropylene-oxide glycol segments orpolytetramethylene-oxide glycol segments are used.

[0019] The hard blocks in the polyester block copolymer preferablyconsist of repeating units of at least one alkylene glycol and at leastone aromatic dicarboxylic acid or an ester thereof. The alkylene groupgenerally contains 2-6 carbon atoms, preferably 2-4 carbon atoms.Examples are ethylene glycol, propylene glycol or butylene glycol.Preferably, use is made of propylene glycol or, butylene glycol. Morepreferably, use is made of butylene glycol. Examples of aromaticdicarboxylic acids are terephthalic acid, isophthalic acid,1,4-naphthalene dicarboxylic acid or 4,4′-diphenyl dicarboxylic acid.Examples of the hard polyester blocks are polyethylene terephthalatesegments, polypropylene terephthalate segments or polybutyleneterephthalate segments. Preferably, polybutylene terephthalate segmentsare used as hard polyester block.

[0020] The ratio between the soft and hard blocks in the polyester blockcopolymer can generally vary within wide limits, but is chosen inparticular in light of the desired hardness of the polyester blockcopolymer. The hardness may generally vary between 20 and 80 Shore D.

[0021] Most preferably, the polyester block copolymer is a blockcopolymer with hard blocks derived from polybutylene terephthalatesegments and soft blocks derived from polytetramethylene-oxide glycolsegments or ethylene oxide-terminated polypropylene-oxide glycolsegments.

[0022] The polyester block copolymer may further contain the customaryadditives such as stabilizers, colorants, processing aids orflame-retarding compounds.

[0023] Examples and the preparation of polyester block copolymers aredescribed inter alia in Handbook of Thermoplastics, ed. O. Olabishi,Chapter 17, Marcel Dekker Inc., New York 1997, ISBN 0-8247-9797-3, inThermoplastic Elastomers, 2nd Ed, Chapter 8, Carl Hanser Verlag (1996)ISBN 1-56990-205-4, and in Encyclopedia of Polymer Science andEngineering, Vol. 12, Wiley & Sons, New York (1988), ISBN 0-471-80944,pp. 75-117 and the references given there.

[0024] The compatibilizer (c) in the thermoplastic elastomer compositionaccording to the invention is compatible with both the dynamicallyvulcanized thermoplastic elastomer (a) and the thermoplastic polyesterblock copolymer (b).

[0025] Compatibilizers that can be used in the thermoplastic elastomercomposition according to the invention are functionalized polymers suchas for instance epoxy or acid functionalized polymers. Preferably theepoxy or acid functionalized polymers are epoxy or acid functionalizedolefine polymers. Examples of epoxy functionalized olefine polymers arecopolymers of ethylene-glycidyl methacrylate or ethylene-glycidylacrylate or terpolymers of ethylene-glycidyl methacrylate-acrylate orglycidyl methacrylate functionalized polyethylene or glycidylmethacrylate functionalized acrylate terpolymers. Examples of acidfunctionalized olefine polymers are maleic anhydride functionalizedolefine polymers such as maleic anhydride functionalized polypropyleneor maleic anhydride functionalized polyethylene. Preferably, an epoxyfunctionalized olefin polymer is used as compatibilizer in thethermoplastic composition according to the invention.

[0026] The thermoplastic elastomer composition according to theinvention for instance contains 20-80 parts (a), 80-20 parts (b) and1-40 parts (c) the sum of the parts (a+b+c) being 100.

[0027] Preferably, the thermoplastic elastomer composition according tothe invention contains 30-70 parts (a), 70-30 parts (b) and 5-20 parts(c), the sum of the parts of (a+b+c) being 100.

[0028] The thermoplastic elastomer composition according to theinvention optionally contains other customary additives. Examples ofsuch additives are reinforcing and non-reinforcing fillers,plasticizers, antioxidants, stabilizers, oil, antistatic agents, waxes,foaming agents, pigments, flame retardants and other known agents andare described in the Rubber World Magazine Blue Book, and in Gaether etal., Plastics Additives Handbook, (Hanser 1990). Examples of fillersthat can be used are calcium carbonate, clay, silica, talc, titaniumdioxide, and carbon. Examples of oil that can be added are paraffinicoil, naphthenic oil or aromatic oil obtained from petroleum fractions.

[0029] Another additive that can optionally be added to thethermoplastic composition according to the invention is a Lewis basesuch as for instance a metal oxide, a metal hydroxide, a metal carbonateor hydrotalcite.

[0030] The additives can be added during the preparation of the TPV orduring the preparation of the thermoplastic elastomer compositionaccording to the invention or during both. The quantity of additive tobe added is known to one skilled in the art.

[0031] The thermoplastic elastomer composition can be prepared via twosuccessive steps but can also be prepared in one step. If thethermoplastic elastomer composition is prepared in two successive steps,in a first step the TPV will be prepared by blending the polypropylenepolymer, the rubber and other additives customarily employed by oneskilled in the art in for instance a Brabender blender. After thesecomponents have been properly dispersed, the vulcanization agent isadded to initiate the dynamic vulcanization. This blend results in aTPV. In a second step the TPV is introduced into an extruder and blendedwith the polyester block copolymer and the compatibilizer. These twosteps can be carried out independently as separate steps or sequentiallyin the same equipment. It is also possible for the thermoplasticelastomer composition according to the invention to be prepared in asingle step, with the TPV, the polyester block copolymer and thecompatibilizer being introduced simultaneously into the extruder and beblended further with the additives customarily employed by one skilledin the art. It is also possible to prepare a TPV in a first step, whichis subsequently blended with a compatibilizer in the same extruder.Next, the resulting TPV masterbatch can be blended with the polyesterblock copolymer.

[0032] The thermoplastic elastomer composition according to theinvention can for instance be blended with one or more polymers chosenfrom styrene-butadiene-styrene rubber (SBS),styrene-ethylene/styrene-butadiene block copolymers (SEBS),styrene-propylene-styrene terpolymers (SPS),styrene-isopropylene-styrene terpolymers (SIPS), polyvinyl chloride,polycarbonate, acrylonitrile-butadiene-styrene terpolymers, polybutyleneterephthalate, polypropylene, styrene-acrylonitrile copolymers,styrene-maleic anhydride copolymers, polyphenylene oxide, orpolyethylene. This for instance involves adding 1-40 parts of theabove-mentioned polymers relative to the parts of the total composition(a+b+c). Preferably, 1-20 parts of the above-mentioned polymers areadded relative to the parts of the total composition (a+b+c).

[0033] The invention also relates to molded articles that contain thethermoplastic elastomer composition according to the invention. Theinvention particularly relates to molded articles comprising a substratepart and a part that comprises the thermoplastic elastomer according tothe invention whereby the parts are being adhered. It has been foundthat the thermoplastic elastomer composition according to the inventionexhibits particularly good adhesion to both polar and apolar substrates.Preferably, the adhesion between the thermoplastic elastomer compositionaccording to the invention and the substrate is such that cohesivefailure takes place, both when the substrate is polar and when it isapolar. Cohesive failure takes place when the adhesion between thethermoplastic elastomer composition according to the invention and thesubstrate is stronger than the thermoplastic elastomer composition.

[0034] The molded articles can be prepared using processing methodscustomarily employed by one skilled in the art, examples beingco-extrusion, blow molding of two or more components, injection moldingof two or more components, robotic extrusion, or injection overmolding.

[0035] The thermoplastic elastomer composition according to theinvention can for instance be used in door profiles, wire & cables,hoses, dashboard films, window encapsulation and soft touch grips.

[0036] The invention will be elucidated with reference to the followingexamples, without being limited thereto.

[0037] The materials used in the examples are the following:

[0038] Arnitel™ EM400 (38 Shore D copolyether ester, DSM)

[0039] Arnitel™ EM550 (55 Shore D copolyether ester, DSM)

[0040] Arnitel™ EM630 (63 Shore D copolyether ester, DSM)

[0041] TPV40 (40 Shore A PP-EPDM-oil TPV)

[0042] Lotader™AX8840 (GMA functionalized PE, Elf Atochem)

[0043] Lotader™AX8860 (terpolymer of ethylene, acrylic ester andglycidyl methacrylate

[0044] (GMA), Elf Atochem)

[0045] Lotader™ AX8930 (GMA functionalized acrylate terpolymer, ElfAtochem)

[0046] The measurements in the examples were carried out using thefollowing tests:

[0047] Hardness DIN 53505

[0048] Mechanical properties ISO 37

[0049] Compression set ISO 815

EXAMPLE 1

[0050] TPV40 is produced by melt blending 45% EPDM, 10% PP, 35%paraffinic oil, 0.5% phenolic resin, 0.5% stannous chloride and 0.5%stabilizer on a 40 mm co-rotating twin screw extruder at a melttemperature of 250° C.

[0051] In a second step the thermoplastic elastomer composition isproduced by melt blending the TPV40 with a copolyether ester (Arnitel™EM400) and an epoxy functionalized compatibilizer (Lotader™ 8860) on a30 mm corotating twin screw extruder at a melt temperature of 230° C.

[0052] The adhesion properties are tested by co-extruding 1 mm strip ofthe thermoplastic elastomer composition on top of different substrates(2 mm of polycarbonate, ABS and polypropylene) at a temperature of 220°C. The adhesion after co-extrusion is evaluated by ranking the peelstrength and is classified as either no, poor or strong adhesion and thetype of failure is classified as either adhesive or cohesive.

[0053] The mechanical properties and adhesion results are shown in table1.

COMPARATIVE EXAMPLE A

[0054] The same procedure as in example 1 is followed but instead of anepoxy functionalized compatibilizer no compatibilizer is used.

[0055] The mechanical properties and adhesion results are shown in table1.

COMPARATIVE EXAMPLE B

[0056] The same procedure as in example 1 is followed but no copolyetherester is added.

[0057] The mechanical properties and adhesion results are shown in table1.

COMPARATIVE EXAMPLE C

[0058] The same procedure as in example 1 is followed but no TPV-40 isadded.

[0059] The mechanical properties and adhesion results are shown intable 1. TABLE 1 Composition A B C 1 Arnitel ™ EM400 50% 90% 50% TPV-4050% 90% 40% Lotader ™ AX8860 10% 10% 10% Mechanical properties Hardness[Shore A] 75  41  96  75 Tensile strength [Mpa]  1.3  3.9  14.1  6.5Elongation [%] 95 310 510 330 Adhesion onto PC Poor No Strong StrongType of failure Adhesive Adhesive Cohesive Cohesive Adhesion onto ABSPoor No Strong Strong Type of failure Adhesive Adhesive CohesiveCohesive Adhesion onto PP Poor Strong No Strong Type of failure AdhesiveCohesive Adhesive Cohesive

[0060] From table 1 it is clear that in comparative examples A, B and Cthere is no or poor adhesion to polar and apolar substrates. The type offailure is in most cases adhesive instead of cohesive. In example 1 verygood adhesion to polar and apolar substrates was found, while the typeof failure was cohesive in every case.

EXAMPLES 2 to 6

[0061] TPV40 is produced by melt blending 45% EPDM, 10% PP, 35%paraffinic oil, 0.5% phenolic resin, 0.5% stannous chloride and 0.5%stabilizer on a 40 mm co-rotating twin screw extruder at a melttemperature of 250° C. In the same extrusion step the copolyether ester(Arnitel™400) and an epoxy functionalized compatibilizer (Lotader™AX8930) are added in different concentrations.

[0062] The adhesion properties are tested by injection molding 30×30×2mm plaques of the thermoplastic elastomer composition against the smallside of 30×30×2 mm plaques of different substrates (polycarbonate, ABSand polypropylene) at a temperature of 240° C. The final part is 60×60×2mm. The adhesion after injection molding is evaluated by cutting testbars across the interface and measuring the mechanical strength of the2K test bar. Besides the adhesion strength, the type of failure isclassified as either adhesive or cohesive.

[0063] The mechanical and adhesion properties are shown in table 2.TABLE 2 2 3 4 5 6 Composition Arnitel ™ 60 50 40 30 20 EM400 TPV-40 2535 45 50 60 Lotader ™ 15 15 15 20 20 AX8930 Mechanical propertiesHardness 80 75 68 63 55 [Shore A] Tensile 7.9 6.7 5.0 4.7 4.0 strength[Mpa] Elongation 490 375 280 200 180 [%] C. set 72 h/ 29 30 30 31 31 23°C. [%] C. set 22 h/ 46 48 51 48 45 70° C. [%] Adhesion to 5.9 5.0 3.73.4 2.9 PC [Mpa] Type of Cohesive Cohesive Cohesive Cohesive Cohesivefailure Adhesion to 5.1 4.3 3.1 2.6 2.1 ABS [Mpa] Type of CohesiveCohesive Cohesive Cohesive Cohesive failure Adhesion to 5.6 4.9 3.8 3.73.1 PP [Mpa] Type of Cohesive Cohesive Cohesive Cohesive Cohesivefailure

[0064] Table 2 shows that the use of a larger amount of Arnitel™EM400 inthe thermoplastic elastomer composition according to the inventionresults in stronger adhesion to both the polar and the apolarsubstrates. In all cases the type of failure is cohesive.

EXAMPLES 7 to 9

[0065] TPV40 is produced by melt blending 45% EPDM, 10% PP, 35%paraffinic oil, 0.5% phenolic resin, 0.5% stannous chloride and 0.5%stabilizer on a 40 mm co-rotating twin screw extruder at a melttemperature of 250° C. In the same extrusion step the epoxyfunctionalized compatibilizer (Lotader ™AX8930) is added.

[0066] In a second step the thermoplastic elastomer composition isproduced by melt blending TPV-40 (including an epoxy functionalizedcompatibilizer, Lotader ™AX8840) with different copolyether esters(Arnitel™ EM400, EM550, EM630) on a 30 mm co-rotating twin screwextruder at a melt temperature of 230° C.

[0067] The adhesion properties are tested by injection molding 2 mmplaques of the thermoplastic elastomer composition against 2 mm plaquesof different substrates (polycarbonate, ABS, polypropylene, Arnitel™ EM550 and polybutylene terephthalate) at a temperature of 240° C. Theadhesion after injection molding is classified as no, poor or strongadhesion. In addition, the type of failure is classified as eitheradhesive or cohesive.

[0068] The mechanical and adhesion properties are shown in table 3.TABLE 3 Composition 7 8 9 Arnitel ™ EM400  50 Arnitel ™ EM550  50Arnitel ™ EM630  50 TPV-40  40  40  40 Lotader ™ AX8930  10  10  10Mechanical properties Hardness [Shore A]  75  86  93 Tensile strength[Mpa]  4.9  5.8  7.0 Elongation [%] 370 300 220 Adhesion to PC StrongStrong Strong Type of failure Cohesive Cohesive Cohesive Adhesion to ABSStrong Strong Strong Type of failure Cohesive Cohesive Cohesive Adhesionto PBT Strong Strong Strong Type of failure Cohesive Cohesive CohesiveAdhesion to Arnitel ™ EM550 Strong Strong Strong Type of failureCohesive Cohesive Cohesive Adhesion to PP Strong Strong Strong Type offailure Cohesive Cohesive Cohesive

[0069] Table 3 shows that the mechanical properties are influenced bythe use of different types of Arnitel™. The adhesion properties,however, are strong for all the substrates. In all cases cohesiveadhesion is obtained.

1. Thermoplastic elastomer composition, characterized in that thecomposition contains: a. a dynamically vulcanized thermoplasticelastomer containing a polypropylene polymer and an at least partlydynamically vulcanized rubber b. a thermoplastic polyester blockcopolymer c. a compatibilizer.
 2. Thermoplastic elastomer compositionaccording to claim 1, characterized in that the composition contains20-80 parts (a), 80-20 parts (b) and 1-40 parts (c), the sum of theparts (a+b+c) being
 100. 3. Thermoplastic elastomer compositionaccording to either of claims 1-2, characterized in that the compositioncontains 30-70 parts (a), 70-30 parts (b) and 5-20 parts (c), the sum ofparts (a+b+c) being
 100. 4. Thermoplastic elastomer compositionaccording to claim 1, characterized in that the polypropylene polymer isa propylene homo- or copolymer.
 5. Thermoplastic elastomer compositionaccording to claim 1, characterized in that the rubber is an EPDM or EPMcopolymer.
 6. Thermoplastic elastomer composition according to claim 1,characterized in that the at least partly dynamically vulcanized rubberhas a gel content that is higher than 80%.
 7. Thermoplastic elastomercomposition according to claim 6, characterized in that the at leastpartly dynamically vulcanized rubber has a gel content that is higherthan 95%.
 8. Thermoplastic elastomer composition according to claim 1,characterized in that the thermoplastic polyester block copolymer is apolyether ester block copolymer.
 9. Thermoplastic elastomer compositionaccording to claim 1, characterized in that the compatibilizer is afunctionalized polymer.
 10. Thermoplastic elastomer compositionaccording to claim 9, characterized in that the functionalized polymeris an epoxy or acid functionalized polymer.
 11. Thermoplastic elastomercomposition according to claim 10, characterized in that the epoxyfunctionalized polymer is an epoxy-functionalized olefin polymer. 12.Molded article that contains the thermoplastic elastomer compositionaccording to any one of claims 1-11.
 13. Molded article comprising asubstrate part and a part that comprises the thermoplastic elastomercomposition according to any of claims 1-11 whereby the parts are beingadhered.